Want to study file, process or network events in macOS? Crescendo is the tool, for Catalina. It’s free and open source too.
From launch, through security checks, TCC and privacy, RunningBoard, to memory management and the Main Event Loop. A comprehensive summary.
Why it takes two clicks or taps to dismiss a dialog which is not the front window in OS X, and why that is correct.
An outline of how apps run, to help you fix their problems, and decide whether more memory would help.